Joint IP/optical layer restoration after a router failure

ABSTRACT

A method and system for providing joint IP/Optical Layer restoration mechanisms for the IP over Optical Layer architecture, particularly for protecting against router failure within such architecture, includes any one of plural node elements participating in the detection and restoration of the joint IP/Optical Layer architecture upon the failure of a router in one of the nodes. The plural node elements may include, but are not limited to, one of plural routers and an optical cross-connect.

FIELD OF THE INVENTION

[0001] The invention generally relates to optical communications andparticularly a method for the restoration of a joint IP/optical layerafter failure of a router therein.

BACKGROUND OF THE INVENTION

[0002] With the Internet rapidly replacing traditional telephonenetworks as the ubiquitous network infrastructure, there isever-increasing consumer demand for greater bandwidth, which translatesto a need for increased system performance. Coping with the continuinghigh growth rate of Internet traffic volume is a significantlychallenging scalability problem. Fiber optics using Wavelength DivisionMultiplexing (WDM) offers the enormous capacity that the Internetrequires to continue to grow at its present and projected future rates.In addition, the increasing agility of the latest Optical LayerCross-Connects (OLXCs) offers the ability to dynamically change theoptical layer connectivity on small time scales. OLXCs have the abilityto convert the wavelength of any incoming channel to any outgoingwavelength (i.e. have wavelength conversion).

[0003] Internet Protocol (IP) network connectivity is more often beingprovided by optical circuits, including OC-48/192, for example. Thus,FIG. 1(a) is a schematic diagram showing the connectivity of IP layer 5to an optical layer 10. FIG. 1(b) shows a more specific schematicdiagram in which IP router 15 may be either hard-wired to Dense WaveDivision Multiplexer (DWDM) 20 for transport, or it may be connected toOLXC 25.

[0004] There is an underlying conflict, however, between the typicaldatagram (connectionless) service that supports the best-effort datadelivery of the Internet and virtual circuit (connection-based) service.This conflict is exacerbated in the world of optical networks, due tothe fixed nature of the wavelengths available and the restoration ofservice in optical networks.

[0005] Optical networks are connection oriented and designed for fixedrate bit streaming with very low error rates. Whereas the Internetemploys soft state where possible, the state of the opticalinfrastructure that is encoded in its OLXCs is hard and must beexplicitly removed. The key elements in the success of the Internet havebeen its simplicity and the flexibility of the Internet service model,and therefore a significant challenge in leveraging the new opticalcapabilities to enhance the Internet and other services is to manage theoptical resources efficiently, without sacrificing the simplicity andflexibility of the Internet.

[0006] In spite of most traffic and media types becoming internetprotocol (IP) based, multiple-hop high-bandwidth optical connectionsreferred to as lightpaths will continue to be of value. Aggregate loadsbetween major metropolitan areas are rather stable, with most of theachievable statistical multiplexing already attained in the regional andcollection (distribution) portion of the network. With electronicswitching systems coping with substantial regional network volumes, thisload can conveniently be assigned to point-to-point lightpaths thatbypass intermediate backbone routers, reducing their load and reducingend-to-end delay and delay variation. Traffic engineering, i.e., loadand quality management, is increasingly performed by adjustingconnectivity and capacity between major backbone gateways on arelatively large time-scale, still small compared to the time-scale ofprovisioning.

[0007] This is both a primary function of, and a significant reasonthat, ATM or Multi-Protocol Label Switching (MPLS) is employed below theIP layer by most network operators. Agile, dynamically configurableOLXCs allow the use of the optical layer directly to implement thesefunctions, avoiding having ATM or MPLS as intermediate layers in futurenetworks. Lightpaths carrying transit traffic, or non-IP traffic, mayremain a significant source of revenue for network operators for theforeseeable future. Whereas much of the transit capacity may carry IPtraffic, operators leasing optical capacity may choose not to disclosethis.

[0008] There are issues involving networks in general as they relate towhere particular service and intelligence are provided. Functionspreviously provided by a SONET/SDH layer.

[0009] SONET(Synchronous Optical NETwork)/SDH (Synchronous DigitalHierachy) is an industry standard for broadband optical fibercommunications. It provides universal optical interfaces at OC-N/STM-Mrate. It also provides integrated OAM&P capabilities within each networkelement which enables fast protection/restoration. A good reference bookis “Understanding SONET/SDH, Standards and Applications” by Ming-ChwanChow, Andan Publisher, 1995.) interposed (not shown) above optical layer10 must be distributed between IP layer 5 and Optical Layer 10 in thearchitecture of FIGS. 1(a) and 1(b), including the recovery of serviceafter equipment failure.

[0010] Restoration may be provided by either the IP layer or the opticallayer 10. The optical layer 10 is able to independently providesub-second protection and/or restoration for link failures, that is whena fiber is cut, and is the most cost-effective solution therefore.However, when a router in the IP/Optical Layer architecture fails, theoptical layer has no independent awareness of the router failure.

[0011] Thus, presently, it is the IP layer 5 that includes the necessaryfunctionality for protecting against router failure. In addition, the IPlayer 5 may include extra link capacity so that the quality of servicemay be preserved in the event of a router failure. As a result, it isthen more cost-effective to use the extra link capacity to protectagainst link failure, and thus there is no incentive to utilize theprotection/restoration function provided by the optical layer 10.Accordingly, IP network operators may choose a restoration strategy thatdepends solely upon the IP layer 5.

[0012] However IP layer restoration systems have some disadvantages. Forinstance, the failure of an unprotected link may result in amean-time-to-repair in the range of four to ten hours althoughmean-time-to-repair for a router failure may be less than one hour.Still, the excessive amount of down-time due to a link failure mayresult in further router failures, which has the potential forsignificant network congestion.

SUMMARY OF THE INVENTION

[0013] Accordingly, the present invention includes a method and systemfor providing joint IP/Optical Layer restoration mechanisms for the IPover Optical Layer architecture, particularly for protecting againstrouter failure within such architecture.

[0014] According to an example embodiment of the present invention, anyone of plural node elements may participate in the detection andrestoration of the joint IP/Optical Layer architecture upon the failureof a router in one of the nodes. The plural node elements may include,but are not limited to, one of plural routers and an opticalcross-connect (OXLC).

[0015] For example, a node element may detect a failure in a lightpathto a node, transmit a request to an optical network to re-establish thelightpath, and reestablish the lightpath using a backup or redundantrouter in place of a failed router at the same node thereof.

[0016] All routers at the nodes are used during normal operations,though, for the purposes of this description, one router may be deemedto be “redundant” since it backs up traffic for another router that hasfailed at the same node. The node element that detects the failed routermay include a router, disposed at another node, whereby the lightpathruns between the detecting router and the failed router; a redundantrouter at the same node as the failed router; or an OXC at the same nodeas the failed router.

[0017] If the router failure is detected by a router, at either a remotenode or at the same node as the failed router, the detecting routertransmits a request to an OXC at the respective node that the lightpathbe re-established using the redundant router in place of the failedrouter. If the detecting router is at the remote node, the OXC at theremote node transmits the request to the OXC at the same node as thefailed router.

[0018] Upon receiving the request for re-establishing the failedlightpath by using the redundant router in place of the failed router,the OXC at the same node as the failed router coordinates there-establishment of all links using the redundant router in place of thefailed router. Also, the OXC at the same node as the failed router mayalso detect the failed router and re-establish links using the redundantrouter in place of the failed router.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1(a) shows a schematic diagram of a joint IP/Optical Layerarchitecture.

[0020]FIG. 1(b) shows a more detailed schematic diagram of a jointIP/Optical layer architecture, including the interconnection optionstherefore.

[0021]FIG. 2 shows an example IP architecture, as part of an exampleembodiment of the present invention, in which a router has failed.

[0022]FIG. 3 shows an example of the IP over Optical Layer architecture,according to an example embodiment of the present invention, in which arouter has failed.

[0023]FIG. 4 shows an example IP architecture, as part of an exampleembodiment of the present invention, in which a path has been re-routedafter a router has failed.

[0024]FIG. 5 is a flow chart showing an example method embodimentaccording to the present invention for a router at a remote node.

[0025]FIG. 6 is a flow chart showing an example method embodimentaccording to the present invention for a router at a home node.

[0026]FIG. 7 is a flow chart showing an example method embodimentaccording to the present invention for an optical cross-connect at ahome node.

DETAILED DESCRIPTION OF THE INVENTION

[0027] As set forth above, FIG. 1(b) illustrates a joint IP/OpticalLayer network node with the optical layer cross-connect (OLXC) 25connected to DWDM 20, to thereby be connected to other OLXCs. Thenetwork node may further include IP router 15, along withdynamically-reconfigurable OLXC 25. Optical lightpaths may beestablished between network elements, via OLXCs, and the lightpathsserve as a virtual circuit.

[0028] In order to facilitate the description of the present inventionthe following network objects are defined.

[0029] A Wavelength Division Multiplexer (WDM) is a system that convertsmultiple optical inputs into narrowly spaced wavelength optical signalswithin an optical amplification band and couples them onto a singlefiber. At the receiving end, the amplified signal may be de-multiplexedand converted to multiple channels of standard wavelength to interfacewith other equipment. It may also be possible to take the wavelengthspecific signals directly as the inputs. In that case, no wavelengthconversion may be necessary at the WDM system. The WDM system may or maynot be integrated with an OLXC.

[0030] A channel is a unidirectional optical tributary connecting twoOLXCs. Multiple channels may be multiplexed optically at the WDM system.One direction of an OC-48/192 connecting two immediately neighboringOLXCs is an example of a channel. A single direction of an Opticalchannel (Och) as defined in ITU-T G.872 between two OLXCs over a WDMsystem is another example of a channel. A channel may generally beassociated with a specific wavelength in the WDM system. However, in aWDM system with transponders, the interfaces to the OLXC may be astandard single color (1310 or 1550 nm). Further, a single wavelengthmay transport multiple channels multiplexed in the time domain. Forexample, an OC-192 signal on a fiber may carry four STS-48 channels. Forthese reasons, a channel may be defined separately from wavelengthalthough in most applications there is a one-to-one correspondence.

[0031] An optical layer cross-connect (OLXC) is a switching element thatconnects an optical channel from an input port to an output port. AnOLXC may also be referred to as an optical cross-connect (OXC), andtherefore shall be referred to as “OXC” hereafter.

[0032] A drop port is an OXC port that connects to the end clientnetwork element (NE). The drop interface may connect the client port tothe OXC drop port. The OXC drop port is essentially a User NetworkInterface (UNI) that connects end devices to the optical layer. The dropport terminates the user network interface between the client NE and theoptical network. It is necessary to distinguish this type of interfacefrom others to identify network requests originating from a client NE.

[0033] A network port is an OXC port that does not directly interfacewith an end client NE. A Network Port in an OXC interfaces with anotherNetwork Port via a WDM system or directly via optical fibers.

[0034] A lightpath is an abstraction of optical layer connectivitybetween two end points. A lightpath is a fixed bandwidth connection(e.g. one direction of a STM-N/OC-M payload or an Och payload) betweentwo network elements (NEs) established via OXCs. A bidirectionallightpath includes two associated lightpaths in opposite directionsrouted over a same set of nodes.

[0035] A source may be a client router physically connected to an OXC byone or more OC-48/192 interfaces. A source may also be a non-IP NEconnected to the OLXC via an OC-48/192 interface. In the case of an IProuter source, the router may have an IP address, and the physicalinterfaces to the OXC are identified with some set of addresses(potentially a single IP address or a unique address per port). In thecase of a non-IP NE, either the NE may be assigned an IP address, or theOLXC port connecting the NE may have an IP address. For non-IP awareequipment interfacing the OLXC, any connection request must beoriginated externally via a proxy or external OS interfaces. Thedestination is essentially the same as the source from the physicalinterface perspective. When a request is generated from one end, theother end client or end OXC interface may become the destination.

[0036] A prominent feature of joint IP/Optical Layer networkarchitecture according to an example embodiment of the present inventionis that every office or node, A-F, in the network includes multiple, orredundant, IP routers 100 _(A) -100 _(F). and a dynamicallyreconfigurable OXC 200 _(A)-200 _(N), as shown in FIG. 3, although thepresent invention is in no way limited thereto. In FIG. 3, however, onlyoffice/node B is shown as having multiple routers 100 _(B1)-100 _(B2),though the present invention is not limited thereto. Rather, it isintended, in the present example embodiment of the invention, that alloffices/nodes have multiple, or redundant, IP routers 100 _(N).

[0037] Each IP office/node may be connected to other offices/nodes byone or more lightpaths. On each link within the network, onechannel/wavelength is assigned as the default routed (one hop)lightpath. The routed lightpath may provide router-to-routerconnectivity over this link. These routed lightpaths may reflect (andare thus identical to) the physical topology. The assignment of thisdefault lightpath is by convention, e.g. the “first” channel/wavelength.All traffic using this lightpath is IP traffic and is forwarded by therouter.

[0038] As shown in FIG. 3, IP routers 100 _(N) at the respectiveoffices/nodes may communicate with their respective OXCs 200 _(N)through a logical interface (not shown). The logical interface defines aset of basic primitives to configure the respective OXC 200 _(N), and toenable the respective OXC 200 _(N) to convey information to therespective router 100 _(N). The mediation device translates the logicalprimitives to and from the proprietary controls of the OXC. A furtherembodiment may integrate the routers and their respective OXC into asingle box or component and use a proprietary interface implementation,while still providing equivalent functionality to the interfacedescribed herein.

[0039] Beyond the node local mechanisms, signaling mechanisms may berequired to construct optical lightpaths. An Application ProgrammingInterface (API) call to create a path may require at least fiveparameters including: destination, wavelength, bandwidth, restorationflag, and a transparency flag. If the restoration flag is set, thelightpath will be protected. Lightpaths without the transparency flagare assumed to carry IP services, and may be rerouted if needed. Oncompletion, an explicit tear down message is sent to remove the path.

[0040] Lightpath services may include lightpath requests between asource and destination, such as an API call with the followingattributes:

[0041] As set forth above, restoration could be done at the IP layer 5and/or the Optical Layer 10, as shown in FIG. 1(a). The presentinvention will be explained in the exemplary context of an ISP centraloffice, using the schematic diagrams of FIGS. 2-4. The IP network ofFIG. 2 includes, at each node therein, at least 2 backbone routers forredundancy, though the detailed office architecture is shown for officeB only. These routers, 100 _(N), aggregate all traffic to or fromrouters that connect to the customers of the IP network.

[0042] Under current IP routing systems, for example, when router 100_(B1) at office/node B fails, IP traffic from office 100 _(A) to 100_(B) would go around offices 100 _(D), 100 _(E), 100 _(F), and 100 _(C)to reach office 100 _(B) via router 100 _(B2), the backup router for 100_(B1). Similarly, traffic from office 100 _(A) to 100 _(C), whichoriginally went through office 100 _(B) would need to go around offices100 _(D), 100 _(E), 100 _(F), and 100 _(C) to reach 100 _(C). Additionalcapacity may therefore be needed on all the inter-office links.

[0043] Under current IP rerouting systems, for example, when router 100_(B), at office/node B fails, IP traffic from office 100 _(A) to 100_(B) would go around offices 100 _(D), 100 _(E), 100 _(F), and 1000 _(C)to reach office 100 _(B) via router 100 _(B2), the backup router for 100_(B1). Similarly, traffic from office 100 _(A) to office 100 _(C) ,which originally went through office 100 _(B) would need to go aroundoffices 100 _(D), 100 _(E), 100 _(F), and 100 _(C) to reach office 100_(C). Additional capacity may therefore be needed on all theinter-office links.

[0044] With the new IP over Optical Layer architecture shown in FIG. 3,according to an embodiment of the present invention, each office/nodemay be equipped with one OXC 200 _(N), which connects to the twobackbone routers 100 _(N1) and 100 _(N2) at the same office/node. Thenall the OXCs 200 _(N) may be connected by a mesh topology. Links betweenrouters are provided by direct lightpaths through the Optical Layer 10,which includes OXC's 200 _(N). In FIG. 3 solid lines represent physicallayer connectivity, and the dotted lines show the OC-48 links that maybe used for the transport of packets between the routers at offices 100_(N) and to the neighboring offices.

[0045] In the restoration scheme according to an embodiment of thepresent invention, when router 100 _(B1) at office B fails, bringingdown both inter-office lightpath link between routers 100 _(A) and 100_(B1) and the lightpath link between routers 100 _(B1) and 100 _(B2),router 100 _(A) may detect that router 100 _(B1) has failed and mayrequest a new connection to be set up to the backup router, R_(B2).Further, OXC_(B) that connects to failed router 100 _(B1) directly maydetect the failure and coordinate the setup of the new lightpath linkbetween routers 100 _(A) and 100 _(B2). This new link may use the sameport for the failed link between routers 100 _(A) and 100 _(B1) onrouter 100 _(A), and either the same port for the failed lightpath linkbetween routers 100 _(B1) and 100 _(B2) on router 100 _(B2), or a spareport on router 100 _(B2). In addition, the bandwidth originally used forthe lightpath link between routers 100 _(A) and 100 _(B1) may be reused,as may the intra-office cabling from router 100 _(A) to OXC_(A) and thecabling from OXC_(B) to 100 _(B2). The restoration for router failures,described above, is implemented in a time period of a couple of seconds.

[0046] More specifically, as shown in FIG. 5, the failure of router 100_(B1) at office/node B (step 500) may be detected by router 100 _(A) atoffice/node A, as in step 505. In step 510, router 100 _(A) may send arequest to OXC_(A), also at node A, to restore the link between routers100 _(A) and 100 _(B1) by setting up a new link (i.e., lightpath)between router 100 _(A) and 100 _(B2). The signaling mechanism in theoptical layer coordinates the lightpath establishment. The request maybe transmitted from OXC_(A) to other OXC's that are on the newlightpath, i.e., OXC_(B) in this case in step 515, and may complete allnecessary switching in OXC_(A) to OXC_(B) to establish the newlightpath. Then, in step 525, upon restoration of the lightpath links tooffice/node B, routing in the IP layer will automatically discover thenew link between 100 _(A) and 100 _(B2), and router 100 _(B1) may bereplaced by router 100 _(B2) for all IP traffic through office/node B,and restoration may be complete at step 530.

[0047] The failure of router 100 _(B1), at step 600, may also bedetected by the redundant router 100 _(B2), which is at the same node asthe failed router, at step 605, as depicted in the flowchart in FIG. 6.In step 610, router 100 _(B2) sends a request to OXC_(B) that itconnects to directly, also at node B, to restore the connection tooffice A by setting up a new lightpath link to routers 100 _(A). In step615, the signaling mechanism may forward the request from OXC_(B) toOXC_(A) to complete all necessary switching to establish the newlightpath. Then, in step 620, upon restoration of the lightpath link tooffice/node A, routing in the IP layer will may automatically discoverthe new link between 100 _(A) and 100 _(B2), and router 100 _(B1) willbe replaced by router 100 _(B2) for all IP traffic through office/nodeB, and restoration may be complete at step 625.

[0048] Further, as shown in the flowchart of FIG. 7, the failure ofrouter 100 _(B1), at step 700, may be detected by the cross-connectOXC_(B), which is disposed at the same office/node B as the failedrouter 100 _(B1) as in step 705. Since OXC_(B) controls connections forall routers at node B, in step 710, OXC_(B) may restore all inter-officelinks associated with failed router 100 _(B1) with router 100 _(B2) viathe signaling mechanisms, thus ending restoration at step 715.

[0049] The IP layer topology resulting from the restoration described inaccordance with the example method embodiments of FIGS. 5-7 above isshown in FIG. 4. As a result of the restoration implementation describedabove, lightpath traffic, as shown in FIG. 4, may utilize lightpath linkfrom router 100 _(A) to router 100 _(B2) using the same number of hopswith no additional backbone capacity required.

[0050] As set forth above, intra-office capacity from cross-connectOXC_(B) to router 100 _(B2), for example, that was formerly used for theintra-office link between routers 100 _(B1) and 100 _(B2) may be reused.Both intra-office lightpath links may require the same amount ofadditional intra-office capacity from the backup router 100 _(B2) to allprovider edge routers. With the restoration scheme described above,lightpath traffic between router 100 _(A) and router 100 _(C), viarouter 100 _(B), now may use the new link between router 100 _(A) androuter 100 _(B2), with one intra-office hop less than an original pathto go across office B and with no additional backbone capacity required.In comparison, IP rerouting would send the traffic via another route,thus potentially requiring additional backbone link capacity and verylikely increasing the hop count.

[0051] Thus, in this example restoration against the failure of router100 _(B1) has been achieved with no requirement for additional backbonebandwidth, OXC ports, or router ports.

[0052] In other cases with different topology, additional ports may berequired on the backup router. For example, if one more backbone link isadded to router 100 _(B1) in the original network shown in FIG. 2, forexample a lightpath link between routers 100 _(E) and 100 _(B1), inaddition to restoring the lightpath link between routers 100 _(A) and100 _(B1) using the new lightpath link between routers 100 _(A) and 100_(B2), the lightpath link between routers 100 _(E) and 100 _(B1) may bereplaced by new lightpath link between routers 100 _(E) and 100 _(B2).Since there is only one port on router 100 _(B2), e.g., the port used bythe failed intra-office lightpath link between routers 100 _(B) and 100_(B2), reusable taken by the lightpath link between routers 100 _(A) and100 _(B2), an port may be required on router 100 _(B2) for the furtherrequired lightpath link between routers 100 _(E) and 100 _(B2). Ingeneral, the minimum number of additional ports needed on the backuprouter equals the total number of inter-office links on the failedrouter reduced by the number of re-usable ports (i.e., same type ofports) on the backup router that can be used by the failed intra-officelinks between the failed router and its backup router.

[0053] After a router failure is repaired, it is desirable to revertback to the normal connections. We describe the details in the followingthree cases:

[0054] No re-use of the wavelength(s) and port(s) of the replacedlightpath

[0055] When a neighbor of the failed router detects that the failure hasbeen repaired, it may first request the replaced lightpath to bere-established using the original wavelength(s) and port(s). After theoriginal lightpath has been restored, it may then request the recoverylightpath to be torn down. This case results in minimum interruption ofthe traffic.

[0056] Re-use of the wavelength(s) without the re-use of the port(s) ofthe replaced lightpath

[0057] When a neighbor of the failed router detects that the failure hasbeen repaired, it may first request the replaced lightpath to bere-established using the original port(s) and new wavelength(s) iffeasible. After the replaced lightpath has been restored, it may thenrequest the recovery lightpath to be torn down. However, if additionalwavelength(s) are not available or if it is required to revert back tothe same wavelength(s) as the one(s) used in the normal condition, therecovery lightpath may need to be torn down first before the originalone gets restored using the original port(s) and wavelength(s). This mayresult in some traffic loss during the reversion process.

[0058] Re-use of the wavelength(s) or port(s) of the replaced lightpath

[0059] When a neighbor of the failed router detects that the failure hasbeen repaired, it may first request the replaced lightpath to bere-established using new port(s) and wavelength(s) if feasible. Afterthe replaced lightpath has been restored, it may then request therecovery lightpath to be torn down. However, if additional wavelength(s)or port(s) is not available or if it is required to revert back to thesame port(s) and wavelength(s) as the ones used in the normal condition,the recovery lightpath needs to be torn down first before the originalone gets restored using the original port(s) and wavelength(s). This mayresult in some traffic loss during the reversion process.

[0060] Note that the restoration mechanisms proposed here are applicableto failure restoration for router interfaces. It is also applicable tocases without backup routers in the same office. Instead, a router in aneighboring office can be used as the backup router.

[0061] While the invention has been described with respect to specificexamples including presently preferred modes of carrying out theinvention, those skilled in the art will appreciate that there arenumerous variations and permutations of the above described systems andtechniques that fall within the spirit and scope of the invention as setforth in the appended claims.

We claim:
 1. A node method of restoring an IP/Optical Layer afterfailure of a router in one of a plurality of nodes, said methodcomprising the steps of: detecting a failure in a path to a first node;transmitting a request to an optical network to re-establish the path;and reestablishing the failed path using a redundant router in place ofa failed router.
 2. The method of claim 1, wherein the path is a lightpath between the first node and a second node.
 3. The method of claim 2,wherein the failure in the path to the other of the plurality of nodesis detected by a router at a second node, and wherein the failed routerand the redundant router are at the first node.
 4. The method of claim2, wherein the failure in the path to the other of the plurality ofnodes is detected by the redundant router at the first node, and whereinthe failed router is at the first node.
 5. The method of claim 2,wherein the failure in the path to the first node is detected by anoptical cross-connect at the first node, and wherein the failed routerand the redundant router are at the first node.
 6. The method of claim3, wherein said transmitting step includes the router at the second nodetransmitting the request to an optical cross-connect at the second nodeto reestablish the path to the first node by using the redundant routerin place of the failed router.
 7. The method of claim 6, wherein saidtransmitting step further includes the optical cross-connect at thesecond node transmitting the request to an optical cross-connect at thefirst node.
 8. The method of claim 4, wherein said transmitting stepincludes the redundant router transmitting the request to an opticalcross-connect at the first node to re-establish the path by using theredundant router in place of the failed router.
 9. The method of claim5, wherein said transmitting step includes the optical cross-connect atthe first node transmitting the request to an optical cross-connect atanother node to re-establish the path by using the redundant router inplace of the failed router at the first node.
 10. A method of restoringan IP/Optical Layer after failure of one of plural routers at a firstnode that further includes an optical cross-connect, said methodcomprising the steps of: a router at a second node detecting a failurein a path between the router at the second node and a router at thefirst node; transmitting a request to an optical network to re-establishthe path; and reestablishing the path using a redundant router in placeof the failed router at the first node.
 11. The method of claim 10,wherein the path is a light path between the first node and the secondnode.
 12. The method of claim 11, wherein said transmitting stepincludes the router at the second node transmitting the request to anoptical cross-connect at the second node to reestablish the path. 13.The method of claim 12, wherein said transmitting step further includesthe optical cross-connect at the second node transmitting the request tothe optical cross-connect at the first node.
 14. A method of restoringan IP/Optical Layer after failure of one of plural routers in a firstnode that further includes an optical cross-connect, said methodcomprising the steps of: a first router at the first node detecting afailure in a path between a second router at the first node and a routerat a second node; transmitting a request to an optical network tore-establish the path; and reestablishing the path using the firstrouter in place of the second router.
 15. The method of claim 14,wherein the path is a light path.
 16. The method of claim 15, whereinsaid transmitting step includes the first router transmitting therequest to an optical cross-connect at the first node to re-establishthe path by using the first router in place of the second router.
 17. Amethod of restoring an IP/Optical Layer after failure of one of pluralrouters in a first node, said method comprising the steps of: an opticalcross-connect at the first node detecting a failure in a path between afirst router at the first node and a router at a second node; andreestablishing the path using a second router in place of the firstrouter at the first node.
 18. A computer-readable medium at a nodemethod of an IP/Optical Layer, said computer-readable medium havingcomputer-executable instructions for performing, after failure of arouter in one of a plurality of nodes, the steps of: detecting a failurein a path to a first node; transmitting a request to an optical networkto re-establish the path; and reestablishing the failed path using aredundant router in place of a failed router.
 19. The computer-readablemedium having computer-executable instructions according to claim 18,wherein the path is a light path between the first node and a secondnode.
 20. The computer-readable medium having computer-executableinstructions according to claim 19, wherein the failure in the path tothe other of the plurality of nodes is detected at a router at a secondnode, and wherein the failed router and the redundant router are at thefirst node.
 21. The computer-readable medium having computer-executableinstructions according to claim 19, wherein the failure in the path tothe other of the plurality of nodes is detected at the redundant routerat the first node, and wherein the failed router is at the first node.22. The computer-readable medium having computer-executable instructionsaccording to claim 19, wherein the failure in the path to the first nodeis detected by an optical cross-connect at the first node, and whereinthe failed router and the redundant router are at the first node. 23.The computer-readable medium having computer-executable instructionsaccording to claim 20, wherein said transmitting step includes therouter at the second node transmitting the request to an opticalcross-connect at the second node to re-establish the path to the firstnode by using the redundant router in place of the failed router. 24.The computer-readable medium having computer-executable instructionsaccording to claim 23, wherein said transmitting step further includesthe optical cross-connect at the second node transmitting the request toan optical cross-connect at the first node.
 25. The computer-readablemedium having computer-executable instructions according to claim 21,wherein said transmitting step includes the redundant routertransmitting the request to an optical cross-connect at the first nodeto re-establish the path by using the redundant router in place of thefailed router.
 26. The computer-readable medium havingcomputer-executable instructions according to claim 22, wherein saidtransmitting step includes the optical cross-connect at the first nodetransmitting the request to an optical cross-connect at another node toreestablish the path by using the redundant router in place of thefailed router at the first node.
 27. An IP/Optical Layer system,comprising: a first router at a first node; a second router at a secondnode that receives a light path transmitted from said first router; anoptical network that receives a request to re-establish the light pathtransmitted from said first router, when said first router determinesthat the light path has failed, and reestablishes the light path using athird router in place of said second router at the second node.
 28. AnIP/Optical Layer system according to claim 27, wherein the first routerdetermines that the light path has failed when the second router fails.29. An IP/Optical Layer system according to claim 28, wherein saidoptical network includes an optical cross-connect at the first node, andsaid optical-cross connect at the first node transmits the request tore-establish the light path to a cross-connect at the second node. 30.An IP/Optical Layer system, comprising: a first router at a first node;a second router at the first node; a third router at a second node thatreceives a light path transmitted from said second router; an opticalnetwork that receives a request to re-establish the light pathtransmitted from said first router, when said first router determinesthat the light path between said second router and said third router hasfailed, and re-establishes the light path using said first router inplace of said second router at the first node.
 31. An IP/Optical Layersystem according to claim 30, wherein the first router determines thatthe light path has failed when the second router fails.
 32. AnIP/Optical Layer system according to claim 31, wherein said opticalnetwork includes an optical cross-connect at the first node, and saidoptical-cross connect at the first node transmits the request tore-establish the light path to a cross-connect at the second node. 33.An IP/Optical Layer system, comprising: a first node having pluralrouters; a second node having plural routers; and an opticalcross-connect disposed at said first router that detects a failure in alight path between a first router in said first node and a first routerin said second node, and reestablishes the light path by using a secondrouter at said first node in place of said first router at said firstnode.